1. Field of the Invention
The invention relates generally to digital controllers for controlling industrial machines and processes, and more particularly, to programmable controllers.
2. Description of the Prior Art
In the simplest system architecture for a programmable controller, the controller includes a processor module and several I/O modules which are supported in the same equipment rack and electrically connected through a backplane circuit board. The backplane circuit board, or simply "backplane" as it is often referred to, is a circuit board with numerous printed circuit paths or traces extending horizontally across the back of the rack to interconnect the modules in the rack.
In a more complex system architecture shown and described in Schultz et al., U.S. Pat. No. 4,413,319, issued Nov. 1, 1983, a programmable controller can also include a stand-alone main processor and a number of "remote" I/O racks strung out along serial communication channels. Schultz et al. disclosed a scanner module that was capable of sending and receiving blocks of I/O status data, using a protocol developed for a high speed serial data channel. The scanner module controlled the processor end of the serial data channel, while at remote locations adapter modules converted the data to the parallel data used by I/O modules. The adapter modules, however, were limited to communicating with the I/O modules through the backplane of an I/O rack. The adapter modules were also limited in that they did not include any user-accessible communication ports.
As technology moves toward greater automation of manufacturing operations, it has become desirable to connect motor controllers to programmable controller systems. Whereas the typical I/O modules of the prior art communicated bytes of I/O status data, motor controllers often utilize blocks of data to provide motor control positioning data or motor operating parameters. Other I/O peripherals which require large groups of data are also being developed. There has not been a general purpose, programmable controller interface module for these more complex I/O devices, with the result that special purpose interfaces were needed to connect these I/O devices to the programmable controller systems mentioned above.